双向循环荷载作用下红土的动强度特性试验研究

发布时间：2018-04-05 21:40

  本文选题：红土　切入点：双向循环荷载　出处：《西北农林科技大学》2017年硕士论文

【摘要】：红土在我国地震频发的南方热带、亚热带地区广泛分布,对该地区红土的动力特性进行研究就显得十分必要,这对其工程抗震设计具有积极的意义。在以往的动三轴试验研究中,学者通常忽略地震纵波产生的拉压动荷载作用,将地震荷载简化为一水平剪切动荷载,在单向振动荷载作用下进行试验,并用最大剪切面上的应力来模拟地震荷载的作用。这种简化方法在深源地震或震级较小的地震中是可行的,但是在浅源地震或震级较大的地震中忽略地震纵波产生的拉压动荷载的影响,是不合理的和偏于不安全的。目前,学者对双向动荷载作用下土体的动力特性研究主要集中在砂土、软黏土和黄土等土类,对红土的研究也多数为在单向振动荷载作用下的试验研究,在双向动荷载作用下对红土的动强度特性研究还较为少见,鉴于此,本文利用SDT-20型微机控制电液伺服土动三轴仪对红土进行了双向振动三轴试验,探究红土在双向循环荷载作用下的动强度特性,主要分析了固结围压、含水率、轴向动荷载幅值、侧向动荷载幅值以及轴向与侧向动荷载间的相位差等因素对红土动强度特性的影响,探究不同的受力状态下红土动强度的变化规律。通过本文试验分析,主要得出以下结论:(1)在相同含水率、相位差、侧向循环荷载幅值条件下,单向和双向动三轴试验中,固结围压对重塑红土动强度的影响规律一致,即在同一循环振次下,固结围压越大,红土的动强度越大。且随着固结围压的增大,相邻两个动强度曲线的间距越来越小,动强度增大的幅度越来越小,增大的趋势也越来越缓慢。(2)不管是在单向还是双向循环荷载作用下,含水率对红土动强度的影响均表现为在相同破坏振次下,红土动强度随含水率的增大而减小,且随着含水率的增大,动强度曲线间距越来越小,动强度降低的速率和幅度也越来越小,最后趋于稳定,含水率对土体动强度的影响也越来越不显著。(3)在同相位试验中(υ=0°),同一循环振次下,红土的动强度随侧向循环荷载幅值的增大而增大,且双向循环荷载下的动强度明显高于单向循环荷载下的值。在变相位试验中,红土的动强度随侧向循环荷载幅值的变化规律整体表现为“正弦”变化现象,即是当相位差υ在0°~90°范围内时,相同循环振次下,动强度随侧向循环荷载幅值增大而增大;当相位差υ在90°~270°范围内时,动强度随侧向循环荷载幅值增大而减小;当相位差υ在270°~360°范围内时,动强度随侧向循环荷载幅值增大而增大。在υ=90°、270°时,随着侧向循环荷载幅值增大,动强度变化规律均表现为先增大后减小,动强度变化趋势由随侧向循环荷载幅值增大而增大的趋势向随侧向循环荷载幅值增大而减小的趋势过渡。(4)相位差在0°~360°范围内增大时,红土动强度以相位差180°为转折点,先减小后增大。υ=180°时的动强度较υ=0°时的动强度有明显的衰减,在同一固结围压下,侧向循环荷载幅值越大,衰减率越大;而在相同的侧向循环荷载幅值下,固结围压越大,衰减率越小。在小围压、大侧向循环荷载幅值以及相位差为180°的条件下,双向动荷载作用对土体的稳定极为不利,实际的工程抗震设计中,应给予足够的重视和充分的考虑。(5)在单向循环振动三轴试验中,cd随含水率的增大而减小,而υd在含水率大于最优含水率时随含水率增大而增大;在双向无相位差的同相位试验中,cd和υd均随含水率的增大而减小,而侧向循环荷载幅值对cd和υd的影响表现为侧向循环荷载幅值越大,cd越小,而υd却越大。
[Abstract]:Red in China's earthquake prone southern tropical and subtropical regions are widely distributed, it is very necessary to research the dynamic characteristics of the laterite area, which is of positive significance to the engineering design. In the past three triaxial test research, scholars usually ignore the earthquake wave generated by the tensile and compressive load. The seismic load is simplified as a horizontal shear load, test in one-way vibration load, and the maximum shear stress on the surface to simulate seismic loads. This simplified method is feasible in the deep earthquakes or smaller magnitude earthquakes, but in shallow earthquakes or large magnitude earthquake ignore the seismic wave produced by tension and compression load effect is not reasonable and safe. At present, research on the dynamic characteristics of the soil under the load of the two-way dynamic mainly concentrated in the sand, soft clay The Loess and other soil types, the research on clay for the most experimental research in one-way vibration load, in the two-way dynamic loading under the dynamic strength characteristics of clay are rare, in view of this, this paper uses SDT-20 type microcomputer controlled electro-hydraulic servo soil three triaxial instrument for the two-way vibration of three axle test the red soil, the dynamic strength properties of clay in the inquiry under the bidirectional cyclic loading, the main analysis of the moisture content, confining pressure, axial dynamic load amplitude, lateral load amplitude and axial and lateral load dynamic phase difference between the influence factors on the dynamic strength properties of clay, explore the changes of different stress state the dynamic strength of clay. Through this analysis, we draw the following conclusions: (1) the rate of phase difference, in the same water, lateral cyclic load amplitude under unidirectional and bidirectional three triaxial test, consolidation confining pressure on remolded red Consistent effect of soil strength, which is in the same number of cycles, the greater the confining pressure, the dynamic strength of clay is greater. And with the increasing of confining pressure, dynamic strength curve of the two adjacent space more and more small, the dynamic range is more and more small intensity increases, the increasing trend is becoming more slowly. (2) whether it is in a one-way or two-way cyclic loading. The effect of moisture content on the dynamic strength of clay were performed in the same vibration times, the dynamic strength increases with the content of clay decreases with water content increasing, the dynamic strength curve of space more and more small, moving rate the amplitude and intensity decreased more and more small, finally stabilized, influence of water content on soil dynamic strength has become increasingly significant. (3) in the same test phase (=0 degrees), the same number of cycles, the dynamic strength of clay increases with the lateral amplitude of cyclic load, and bidirectional The dynamic strength under cyclic load was significantly higher than that of unidirectional cyclic loading. In the test phase, the dynamic strength of clay's overall changes with the lateral cyclic load amplitude is the sine change phenomenon, that is when the phase difference V at 0 DEG ~90 DEG range, the same number of cycles, dynamic the strength increases with the increase of the lateral amplitude of cyclic load; when the phase difference V at 90 DEG ~270 DEG range, the dynamic strength with the lateral amplitude of cyclic load increases; when the phase difference V at 270 DEG ~360 DEG range, the dynamic strength increases with the increase of lateral cyclic load amplitude. At =90 DEG, 270 degrees, with lateral cyclic load amplitude increases, the change rule of dynamic strength increased first and then decreased, the dynamic strength change trend with the lateral amplitude of cyclic load by increasing the amplitude of cyclic load to side with increasing trend (4) phase transition. 鍦，

本文编号：1716601